As an example, I have used the absolute value function abs but I could have used abs($_). Which is best? Does it matter?

It doesn't really matter which you use - either way, the same code gets executed.

Interestingly, there's no need to call on the abs() function at all.
You could replace: 
my @digits = split //, abs;
with:
my @digits = split //, $_;

[download]
That will work fine because the "-" character evaluates to zero in numeric context, anyway.
With that change (and the other previously mentioned correction) in place, the script then outputs: 
C:\_32\pscrpt>perl try.pl
Argument "-" isn't numeric in addition (+) at try.pl line 10.
Argument "-" isn't numeric in addition (+) at try.pl line 10.
Argument "-" isn't numeric in addition (+) at try.pl line 10.
-221 -21 1 1 3 5 21 34 89 144

[download]
The warnings can be silenced by inserting: 
no warnings 'numeric';

[download]
into the oddDigitSum() subroutine: 
sub oddDigitSum {
    no warnings 'numeric';
    my @ans;
    for(@_) {
        my @digits = split //, $_;
        my $sum;
        $sum += $_ for @digits;
        $sum % 2 && push @ans, $_;
    }
    return @ans;
}

[download]
Note that any "numeric" warnings triggered from outside the oddDigitSum() subroutine are still enabled.

I'm not sure which approach is the most efficient - you could use Benchmark; to find out, if you want.
I expect there's not much difference performance-wise.

Cheers,
Rob

In reply to Re: Newbie question by syphilis
in thread Newbie question by oldB51

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.